... After reboot you have no ramdisk, and the Volume Group is incomplete
(because you didn't removed PV on ramdisk).

And this is no different than if snapshot was on any other device such
as esata-hdd, usb-hdd or usb stick. LVM should handle this. If the
snapshot device goes away, then just vgreduce it on the reboot.
Trying to retrofit snapshot into existing systems is far easier if you
can use ramdisk, esata-hdd, usb-hdd, usb-stick because most systems have
allocated all space and rather than struggling through trying to compact
and reduce VG, LV, PV, partition, filesystem to gain space it is much
easier to use other devices. And again this is something that LVM
should be able to handle.

If there is only snapshot, you can recover it, if some operation placed
here part of another volume, you will lose data.

part of another volume placed where? on the snapshot? I don't
understand this part.